xcorr2_fft(A,B) computes the cross-correlation of matrices A and B using the FFT algorithm.
When matrices A and B are real, xcorr2_fft is numerically equivalent to xcorr2, but much faster.
For big matrices, the speed improvement can be up to 100 times!
The correlation is simply evaluated padding matrices a and b with zeros according to the size of the correlation map. In this way, the periodicity of the circular cross-correlation evaluated with the FFT becomes equivalent to the linear cross-correlation evaluated with conv2.
a = rand(122); b=rand(332);
a = a-mean(a(:));
b = b-mean(b(:));
tic,cl = xcorr2(a,b);toc
Elapsed time is 0.223502 seconds.
tic,cf = xcorr2_fft(a,b);toc
Elapsed time is 0.030935 seconds.
ans = 4.1922e-13
Alessandro Masullo (2021). xcorr2_fft(a,b) (https://www.mathworks.com/matlabcentral/fileexchange/53570-xcorr2_fft-a-b), MATLAB Central File Exchange. Retrieved .
Try it with >1000 x1000 matrices is devastes matlab's time by minutes.
Great! By converting apad and bpad on lines 37-38 to gpuArray the code also has gpu compatibility!
I must admit, I was shocked by the speed.
Well done!! Very useful!
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